AGT-5: Transitions

A finding of AGT-5 means that a transition of the machine leads nowhere, that a state can’t be reached, or that a state with always can’t settle. The rules page says what the rule checks.

Messages

<file>:<line>: error: initial: initial state <state> does not exist (AGT-5)
<file>:<line>: error: <path>: target state <state> does not exist (AGT-5)
<file>:<line>: error: states.<state>.always: always transitions loop: <states>. smllm leaves a state with always at once, so the loop might never stop. Break it with an event (AGT-5)
<file>:<line>: warning: states.<state>: state <state> is unreachable. Add a transition to it, or set meta.entryPoint: true (AGT-5)
<file>:<line>: warning: <path>: reenter has no effect without a target, because a transition without one never re-enters. To re-enter it, add target: <state> (AGT-5)
<file>:<line>: warning: states.<state>: smllm leaves a state with always at once, so it never offers the state's on events (AGT-5)

Cause

Each message has its own cause, and smllm validate lists the last three, the warnings, only with --warnings:

• initial names a state that the machine doesn’t have.
• A transition’s target names a state that the machine doesn’t have. A misspelt or renamed state is the usual cause.
• States with always transitions lead back to the state where they started, so smllm would pass through them forever.
• No transition leads to a state, and the state isn’t an entry point, so no instance can ever be in it.
• A transition sets reenter: true but has no target. A transition without a target leaves the instance where it is, and never re-enters the state.
• A state has both always and on. smllm leaves the state at once, so the agent never gets the chance to fire its events.

Fix

Fix each message in the order of the causes:

• Set initial to the name of a state.
• Correct the target to the name of a state, or add the state.
• Give one of the states of the loop an event that the agent fires, in place of its always transition.
• Add a transition to the state, or mark the state with meta: { entryPoint: true } if the agent enters it directly. Delete a state that nothing uses.
• Set target to the state itself, so that the transition re-enters it and runs its exit and entry actions again.
• Move the events of on to a state that the agent waits in, or remove the always transitions.

Example

The event reproduced of this machine leads to FIXING, but the state is called FIX:

.smllm/fix.smllm.yaml

id: fix
initial: TRIAGE
meta:
  smllm: 1
states:
  TRIAGE:
    on:
      reproduced: FIXING
  FIX:
    on:
      fixed: DONE
  DONE:
    type: final

smllm validate --warnings reports the missing state. It also warns that nothing leads to FIX, and so to DONE:

$ smllm validate --warnings .smllm/fix.smllm.yaml
.smllm/fix.smllm.yaml:8: error: states.TRIAGE.on.reproduced: target state FIXING does not exist (AGT-5)
.smllm/fix.smllm.yaml:9: warning: states.FIX: state FIX is unreachable. Add a transition to it, or set meta.entryPoint: true (AGT-5)
.smllm/fix.smllm.yaml:12: warning: states.DONE: state DONE is unreachable. Add a transition to it, or set meta.entryPoint: true (FMT-2)
1 error, 2 warnings, 0 info
[exit 1]

The warning for DONE ends with (FMT-2), not (AGT-5), because DONE is a final state. A final state that no instance can reach breaks the rule for final states, so smllm reports it under FMT-2.

The fixed machine leads to FIX:

.smllm/fix.smllm.yaml

id: fix
initial: TRIAGE
meta:
  smllm: 1
states:
  TRIAGE:
    on:
      reproduced: FIX
  FIX:
    on:
      fixed: DONE
  DONE:
    type: final

smllm validate reports no finding:

$ smllm validate --warnings .smllm/fix.smllm.yaml
0 errors, 0 warnings, 0 info